Miniature MEMS Condenser Microphone Package and Fabrication Method Thereof

ABSTRACT

MEMS microphone packages and fabrication methods thereof are disclosed. A MEMS microphone package includes a casing with a conductive part disposed over a substrate, to enclose a cavity. A MEMS acoustic sensing element and an IC chip are disposed inside the cavity. An opening with an acoustic passage connects the cavity to an ambient space. A first ground pad is disposed on a backside of the substrate connecting to the conductive part of the casing through a via hole of the substrate. A second ground pad is disposed on the backside of the substrate connecting to the MEMS acoustic sensing element or the IC chip through an interconnection of the substrate, wherein the first ground pad and the second ground pad are isolated from each other.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-In-Part of pending U.S. patentapplication Ser. No. 12/689,283, filed on Jan. 19, 2010 and entitled“Miniature MEMS Condenser Microphone Packages and Fabrication MethodThereof”, the teachings of which are incorporated herein by reference,which claims the benefit of U.S. Provisional Application No. 61/145,826,filed on Jan. 20, 2009, the entirety of which are incorporated byreference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to micromachined acoustic device packages and inparticular to micromachined miniature MEMS microphone packages andfabrication methods thereof.

2. Description of the Related Art

Micromachined silicon microphones have been disclosed in many patents.For example, U.S. Pat. Nos. 5,619,476, 5,870,351, 5,894,452 and6,493,288 disclose capacitive-type ultrasonic transducer fabricationmethods. U.S. Pat. Nos. 5,146,435; 5,452,268; 6,535,460 and 6,870,937disclose micromachined capacitive transducers that are mainly used forsound pickups. In these patents, however, inventiveness has focused onthe design and manufacturing of micromachined microphone dies. In otherwords, inventiveness has focused on the wafer level processing ofmicrophones.

For microphones to be used in any type of electronic devices, properhousing needs to be provided such that the microphone dies can be housedin a suitable package to prevent it from environmental interferences.Preferably, this housing structure also shields the sensing elements ofa silicon microphone from outside electromagnetic interferences. Also,the packaged microphones need to have contact leads, such that thecontact leads can be soldered onto an electronic board where they areused. Lastly, the packaging method used for the microphones, must be lowcost and allow for mass production.

Compared with traditional electret microphones, micromachined MEMSmicrophones have the advantage of being able to sustain high re-flowtemperatures. Thus, to minimize electronic product assembly costs, themicromachined MEMS microphones are packaged in form factors that allowfor the surface mounting of microphones to a PCB board.

Several packaging methods for MEMS microphones have been disclosed. U.S.Pat. No. 6,781,231, the entirety of which is hereby incorporated byreference, discloses a micro-electro-mechanical system package includinga micro-electro-mechanical system microphone, a substrate, and a cover.The substrate has a surface for supporting the micro-electro-mechanicalmicrophone. The cover includes a conductive layer having a centerportion bounded by a peripheral edge portion. A housing element isformed by connecting the peripheral edge portion of the cover to thesubstrate. The center portion of the cover is spaced from the surface ofthe substrate to accommodate the micro-electro-mechanical systemmicrophone. The housing includes an acoustic port for allowing anacoustic signal to reach the micro-electro-mechanical system microphone.U.S. Patent application publication 2005/0018864, the entirety of whichis hereby incorporated by reference, discloses a silicon condensermicrophone package comprising a transducer unit, a substrate, and acover. The substrate includes an upper surface having a recess formedtherein. The transducer unit is attached to the upper surface of thesubstrate and overlaps with at least a portion of the recess wherein aback volume of the transducer unit is formed between the transducer unitand the substrate. The cover is placed over the transducer unit andincludes an aperture.

U.S. Pat. No. 7,434,305, the entirety of which is hereby incorporated byreference, discloses a silicon condenser microphone package comprising atransducer unit, substrate, and a cover. The substrate includes an uppersurface having a recess formed therein. The transducer unit is attachedto the upper surface of the substrate and overlaps with at least aportion of the recess wherein a back volume of the transducer unit isformed between the transducer unit and the substrate. The cover isplaced over the transducer unit and includes an aperture.

U.S. Pat. No. 7,439,616, the entirety of which is hereby incorporated byreference, discloses a silicon condenser microphone package including atransducer unit, a substrate, and a cover. The substrate, including anupper surface transducer unit, is attached to the upper surface of thesubstrate and overlaps with at least a portion of the recess wherein aback volume of the transducer unit is formed between the transducer unitand the substrate. The cover is placed over the transducer unit andeither the cover or the substrate includes an aperture.

The mentioned packaging methods provide a silicon condenser microphonepackage that allows acoustic energy to contact a transducer disposedwithin a housing. The housing provides necessary pressure references,while at the same time, protects the transducer from light,electromagnetic interference and physical damage. The mentionedpackaging methods, however, fail to critically address aspects ofpackaged microphones related to usage and assembly thereof. Some aspectsinclude, but are not limited to, acoustic leakage through sidewallsand/or a cover of the microphone package, secure microphone attachmentto an underlying PCB board, effectiveness of shielding fromelectromagnetic interference, electronic signal transmission distortionfrom the microphone package to the underlying PCB board, flexibility ofa packaged microphone for surface mounting, and ease of manufacturingfor volume production, etc.

BRIEF SUMMARY OF THE INVENTION

An embodiment of the invention provides a MEMS microphone package,comprising: a casing with a conductive part disposed over a substrate,to enclose a cavity; a MEMS acoustic sensing element and an IC chipdisposed inside the cavity; an opening comprising an acoustic passageconnecting the cavity to an ambient space; a first ground pad disposedon a backside of the substrate connecting to the conductive part of thecasing through a via hole of the substrate; a second ground pad disposedon the backside of the substrate connecting to the MEMS acoustic sensingelement or the IC chip through an interconnection of the substrate,wherein the first ground pad and the second ground pad are isolated fromeach other.

Another embodiment of the invention provides a method for fabricating aMEMS microphone package, comprising: providing a substrate; forming aMEMS sensing element and an IC chip on the substrate; disposing a casingwith a conductive part on the substrate, to enclose a cavity toaccommodate the MEMS sensing element and the IC chip; forming an openingcomprising an acoustic passage connecting the cavity to an ambientspace; and connecting the conductive part of the casing to a firstground pad on the backside of the substrate through a via hole;connecting the MEMS acoustic sensing element or the IC chip to a secondground pad on the backside of the substrate through an interconnection,wherein the first ground pad and the second ground pad are isolated fromeach other.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the subsequentdetailed description and examples with references made to theaccompanying drawings, wherein:

FIGS. 1A-1C are cross sections of some embodiments of MEMS microphonepackages, being surface-mounted on a supporting PCB substrate;

FIGS. 2A and 2B are cross-sectional views of a microphone package,without the casing, according to one embodiment of invention;

FIG. 3 is a top view of a microphone package according to one embodimentof the invention;

FIG. 4 is a top view of a microphone package according to anotherembodiment of the invention;

FIG. 5 is a cut-out view of the casing of the microphone package alongthe AA′ line in FIG. 3 according to one embodiment of the invention;

FIG. 6 is an illustration of acoustic wave propagation in amulti-layered structure;

FIG. 7 schematically shows an acoustic wave transmission in athree-layered panel;

FIG. 8 is the estimated transmission loss in the three-layered panel asillustrated in FIG. 7;

FIG. 9 is a detailed view of a side wall of a microphone packageaccording to one embodiment of the invention;

FIGS. 10A-10C are cross sections of some embodiments of MEMS microphonepackages, being surface-mounted on a supporting PCB substrate; and

FIGS. 11A-11C are cross sections of some embodiments of MEMS microphonepackages, being surface-mounted on a supporting PCB substrate.

DETAILED DESCRIPTION OF THE INVENTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof various embodiments. Specific examples of components and arrangementsare described below to simplify the disclosure. These are merelyexamples and are not intended to be limiting. In addition, thedisclosure may repeat reference numerals and/or letters in the variousexamples. This repetition is for the purpose of simplicity and clarityand does not in itself indicate a relationship between the variousembodiments and/or configurations discussed. Moreover, the formationmethod for a first feature over or on a second feature in thedescription that follows may include embodiments in which the first andsecond features are formed in direct contact or not in direct contact.

Main features and key aspects of embodiments of the invention provide aMEMS microphone package having a conductive casing that is electricallyconnecting to a common analog ground lead of a supporting PCB motherboard to shield a sensing element from the environment andelectromagnetic interferences. In one embodiment, a MEMS microphonepackage has strong bonding strength between a microphone package and asupporting PCB substrate due to the connection of a conductive casing toa supporting PCB substrate. Embodiments of the invention also provide aMEMS microphone package that is not vulnerable to temperaturefluctuations which may occur during the packaging and assembly process.Other embodiments of the MEMS microphone package of the inventionfurther enhance acoustic signal transmittances to the sensing elementhoused in the package.

The foregoing and other objectives of the invention are achieved by asurface mountable MEMS microphone package including a transducerelement, IC chips and other passive elements supported by a substratehoused in a cavity formed by the substrate. A housing wall and a covermember have an opening to allow acoustic signals to pass therethroughand reach the membrane of a MEMS sensing element. The substrate, housingwall and the cover member are stacked and bonded together to form acavity that minimally alters the acoustic response of the MEMS sensingelement. A conductive casing is provided surrounding and enclosing thehousing wall and cover plate of the microphone package. An acousticabsorbing material is provided and interposed between the conductivecasing and the housing wall as well as the top cover plate of themicrophone package. The conductive casing can be soldered to a PCBsubstrate that supports the microphone package, and electricallyconnecting to a common analog ground lead on the PCB substrate to form ashield for the microphone from the environment and electromagneticinterferences.

Meanwhile, a different approach is disclosed for packaging of the MEMSmicrophone when compared to prior art. The package of the MEMSmicrophone of the invention is both acoustically sound and massproducible. The MEMS microphone of the invention can be considered as anindividual device and an integral component. The packaging methodaccording to some embodiments of the invention minimally alters theacoustic response of a microphone after it is packaged. At the sametime, the packaging method outlined according to some embodiments of theinvention provides minimal distortion for the transmission of electronicsignals from the packaged microphone to an attached motherboard. Themicrophone package according to some embodiments of the inventionprovides mechanical shielding from the environmental and electromagneticinterferences.

Referring now to FIG. 1A, an embodiment of a MEMS microphone package 100a includes a substrate 10 for which a MEMS acoustic sensing element 3,an IC chip 4 and passive component 5 are mounted. An acoustic cavity 6is formed by the substrate 10, housing walls 20 and a cover member 40.The attachment of the housing wall 20 and the cover member 40 to thesubstrate 10 is realized using glue 30 which is applied between thesubstrate 10 and the housing wall 20, and between the housing wall 20and the cover member 40. The height of the housing wall 20 is largeenough such that there is enough clearance 11 between the top surface ofMEMS sensing element 3 and the cover member 40. Soldering pads 2 areformed at the bottom of the substrate 10 to allow the packaged MEMSmicrophone to be surface mounted onto the PCB mother board 70. Thesubstrate 10 can be made of FR-4 material to match the thermal propertyof the PCB mother board 70. The cover member 40 has an opening 1A toallow acoustic signals to pass therethrough to reach the surface of MEMSsensing element 3. In one embodiment, the opening 1A is formed in andextended through the cover member 40. The opening 1A comprises anacoustic passage 17 connecting the cavity to an ambient space. Thelocation of the opening 1A is chosen such that it is away from thesensing element 3 to protect dust from falling onto or moisture, such asfrom the mouth of a human, to reach the surface of the sensing element3.

Referring to FIG. 1A, further, a conductive casing 50 surrounds andencloses the microphone package. In one embodiment, an acoustic opening15, formed in the conductive casing 50, is aligned with the opening 1Ato allow acoustic signals to pass therethrough. An acoustic absorptionlayer 60 is inserted between the microphone housing wall 20 and/or topcover member 40 and the conductive casing 50. The conductive casing 50is not directly connecting to either the analog or digital ground of themicrophone package, it is instead electrically connecting to a commonanalog ground lead on a PCB mother board 70 through soldering pads 52.

While the casing 50 is made of metal or other electrically conductivematerials, the housing wall 20 and the cover member 40 are generallymade of plastics or FR-4 materials that are electrically insulated. Theacoustic absorption material 60 may comprise foam, cork, sponge, rubber,or spray-on silicone coating.

According to another embodiment of the invention, a method forfabricating a MEMS microphone package is provided. The fabricationmethod comprises the steps of providing a substrate, and forming acavity enclosed by a top cover part, wherein a housing wall partsurrounds and supports the top cover part, and the substrate supportsthe housing wall part and the cover part. Also, a MEMS sensing elementand an IC chip is formed inside of the cavity and an opening comprisingan acoustic passage connecting the cavity to an ambient space is formedalong with a conductive casing to enclose the top cover part and thehousing wall. The conductive casing is soldered to a PCB mother boardand is electrically connecting to a common analog ground lead on the PCBmother board.

FIG. 1B is a cross section of another embodiment of the MEMS microphonepackage. In FIG. 1B, a MEMS microphone package 100 b includes a casing150 a with a conductive part disposed over a substrate 10 (also referredto as a MIC substrate), to enclose a cavity 11. The casing 150 a can bea unitary metal casing attached onto the substrate 10 by using aconductive glue 30. A MEMS acoustic sensing element 3, an IC chip 4, andat least one passive component 5 can be disposed inside the cavity 11.An opening 1A with an acoustic passage connects the cavity 11 to anambient space. A first ground pad 130 (also referred to as an analogground pad) is disposed on a backside of the substrate 10 connecting tothe conductive part of the casing 150 a through a via hole 120 (e.g., athrough silicon via (TSV)) in the substrate 10. A second ground pad 140(also referred to as a digital ground pad) is disposed on the backsideof the substrate 10 connecting to the MEMS acoustic sensing element 3 orthe IC chip 4 through an interconnection 160 or a redistribution line(RDL) embedded in the substrate 10, wherein the first ground pad 130 andthe second ground pad 140 are isolated from each other. Since thedigital signals and environmental interferences are respectivelygrounded, cross talk effect and environmental electromagneticinterference (EMI) noise can be eliminated. Therefore, a clean and clearacoustic signal can be received by the MEMS microphone package 100 b.

In one embodiment of the invention, the substrate 10 is soldered onto aPCB mother board 70 (also referred to as a system PCB mother board),wherein the first and second ground pads 130 and 140 are soldered to acommon ground pad 170 on the PCB mother board 70. In another embodimentof the invention, the substrate 10 is soldered onto a PCB mother board70, wherein the first and second ground pads 130 and 140 are soldered torespective different ground pads on the PCB mother board. Other contactpads 135 on the backside of the substrate 10 can be soldered with thecorresponding solder pads 175 on the PCB mother board 70.

FIG. 1C is a cross section of another embodiment of the MEMS microphonepackage. In FIG. 1C, a MEMS microphone package 100 c includes a casing150 b with a conductive part disposed over a substrate 10 (also referredto as a MIC substrate), to enclose a cavity 11. The casing 150 b can bea multilayered casing attached onto the substrate 10 by using aconductive glue 30. The multilayered casing 150 b can include a topcover part 155 and a housing wall part 153 surrounding and supportingthe top cover part. In another embodiment, the multilayered casing caninclude a conductive layer 154 sandwiched between two non-conductivelayers 152 and 156. Note that the multilayered casing may furtherinclude an acoustic absorption layer lining the multilayered casing. AMEMS acoustic sensing element 3, an IC chip 4, and at least one passivecomponent 5 can be disposed inside the cavity 11. An opening 1A with anacoustic passage connects the cavity 11 to an ambient space. A firstground pad 130 is disposed on a backside of the substrate 10 connectingto the conductive part of the casing 150 b through a via hole 120 (e.g.,a through silicon via (TSV)) in the substrate 10. A second ground pad140 is disposed on the backside of the substrate 10 connecting to theMEMS acoustic sensing element 3 or the IC chip 4 through aninterconnection 160 or a redistribution line (RDL) embedded in thesubstrate 10, wherein the first ground pad 130 and the second ground pad140 are isolated from each other.

In one embodiment of the invention, the substrate 10 is soldered onto aPCB mother board 70, wherein the first and second ground pads 130 and140 are soldered to a common ground pad 170 on the PCB mother board 70.In another embodiment of the invention, the substrate 10 is solderedonto a PCB mother board 70, wherein the first and second ground pads 130and 140 are soldered to respective different ground pads on the PCBmother board. Other contact pads 135 on the backside of the substrate 10can be soldered with corresponding solder pads 175 on the PCB motherboard 70.

An exemplary embodiment of a microphone package without the casing 50 isillustrated in FIG. 2A. The housing wall 20 is typically glued togetherwith the substrate 10 and the cover member 40. Alternatively, such aswhen using plastic materials for the housing wall 20 and the covermember 40, the housing wall 20 and the cover member 40 can form asingle-pieced cover member 40, as shown in FIG. 2B. The cover member 40is then, again glued to the substrate 10. When manufactured, the covermember 40, housing wall 20 and substrate 10 can be laminated together.In such a case, then, the glue 30 is a lamination agent that allows thecover member 40 to bond to the housing wall 30 and subsequently, thesubstrate 10.

The cover member 40 and the housing wall 20 may be a single layeredmaterial, such as plastics, or multi-layered materials, such as FR-4materials. In either case, there is no need to sandwich a layer ofconductive material in between the multi-layered materials. The need forthe cover member 40 and the housing wall 20 is that they form a cavitythat is rugged enough to house the MEMS sensing element 3, a passivecomponent 5 and an IC chip 4. It is preferable, though, that the covermember 40 and the housing wall 20 have high acoustic impedance.

FIG. 3 schematically shows the top view of the casing 50, according toone embodiment of the invention. A through hole 1A is cut through thecasing 50 to allow the passage of acoustic pressure waves. The casing 50has a top surface 53 and an edge rail 51, is typically made of sheetmetals such as aluminum or other conductive materials. The casing 50 mayalso be made of multi-layered material. In which case, though, at leastone layer of material needs to be electrically conductive. FIG. 4schematically shows a top view of the casing 50 according to anotherembodiment of the invention. Here, the edge rail 51 is not continuous,but it can still be made of the same material as the top surface 53 ofthe casing 50.

FIG. 5 schematically shows a cut-out view of the microphone packagetaken along the AA′ line in FIG. 3. The acoustic absorption layer 60 maybe coated on the inside surface of the casing 50. At the bottom of edgerail 51, a soldering pad 52 is needed to attach the entire casing 50securely to a PCB mother board 70, as shown in FIG. 1. The soldering pad52 is electrically conductive to make the casing 50 electricallyconnecting to a common analog ground lead on the PCB mother board 70. Asnoted earlier, the acoustic absorption layer 60 may be made of foam,cork, sponge, rubber, or spray-on silicone coating. For easy assembly,the acoustic absorption layer 60 may be first attached to the casing 50,as shown in FIG. 5.

One of the big technical issues for a packaged microphone is its abilityto shield out unwanted acoustic noises. These noises are sometimesleaked through the side wall and the top cover of a microphone to reachthe sensing element. Another embodiment of a multi-layered panel isconsidered as shown in FIG. 6. For a normal plane wave incidence, atransmission coefficient is given by:

$T = \frac{{m_{11}m_{22}} - {m_{12}m_{21}}}{m_{22}}$${where},{\begin{bmatrix}m_{11} & m_{12} \\m_{21} & m_{22}\end{bmatrix} = {T_{n}T_{n - 1}\mspace{14mu} \ldots \mspace{14mu} T_{0}}}$$T_{n} = {\frac{1}{2}\begin{bmatrix}{\left( {1 + \frac{z_{n}}{z_{n + 1}}} \right)^{{{({k_{n} - k_{n - 1}})}}d_{n}}} & {\left( {1 - \frac{z_{n}}{z_{n + 1}}} \right)^{{- {{({k_{n} + k_{n + 1}})}}}d_{n}}} \\{\left( {1 - \frac{z_{n}}{z_{n + 1}}} \right)^{{{({k_{n} + k_{n + 1}})}}d_{n}}} & {\left( {1 + \frac{z_{n}}{z_{n + 1}}} \right)^{{- {{({k_{n} - k_{n - 1}})}}}d_{n}}}\end{bmatrix}}$

and Z_(n)=ρ_(n)c_(n) is the impedance, k_(n)=ωc_(n) is the wave numberof the n^(th) layer, and d_(n) is the position of the interface, asshown in FIG. 6. For viscoelastic materials, the C is given by:

$c_{n} = \left( \frac{{3{G_{B}(\omega)}} + {4{G_{S}(\omega)}}}{3\rho_{n}} \right)^{1/2}$

where, G_(B)(ω) and G_(S)(ω) are, respectively, the complex bulk andshear modulus.

The transmission loss can then be calculated through:

TL=20 log|t(ω)|

where the frequency dependence of the transmission coefficient isexplicitly indicated.

For a three-layered panel (glass-polymer-glass) as shown in FIG. 7, thetransmission loss is a function of frequency and is plotted in FIG. 8.Here h is the thickness of each layer. The material and geometricparameters used in the calculation are given below:

h₁ = h₃ = 1.5 mm, h₂ = 2.2 mmρ₀ = ρ₄ = 1.2  kg/m³, ρ₁ = ρ₃ = 2461  kg/m³, ρ₂ = 1115  kg/m³${c_{0} = {c_{4} = {340\; {m/\sec}}}},{c_{1} = {c_{3} = {5770{m/\sec}}}},{c_{2} = \left( \frac{{3{G_{B}(\omega)}} + {4{G_{S}(\omega)}}}{3\rho_{n}} \right)^{1/2}}$G_(S)(ω) = μ_(∞) + (μ₀ − μ_(∞))[1 + (ω τ₀)^(1 − α)]^(β)${G_{B}(\omega)} = {{\frac{2{{vG}_{S}(\omega)}}{1 - {2v}}_{v = 0.4}} = {4{G_{S}(\omega)}}}$μ_(∞) = 2.35 × 10⁸Pa μ₀ = 4.79 × 10⁵Pa α = 0.46 β = −0.1946τ₀ = 0.3979sec 

The results in FIG. 8, indicate that with a three-layered structure asshown in FIG. 7, it is possible for a micromachined MEMS microphonepackage to achieve a 20 dB reduction in noise at a frequency level of 1kHz.

Referring to the FIG. 9, a section of a packaged microphone side walland the top cover is schematically illustrated. The acoustic absorptionlayer 60 is sandwiched between the casing 50 and the housing wall 20. Incomparison with FIG. 8, it is easy to identify that this sandwichedstructure is similar to the three-layered structure illustrated in FIG.8. In a typical microphone package, though, the thickness of the casing50 is usually about 0.05 mm to 0.2 mm thick. And the thickness of thehousing wall 20 varies from 0.1 mm to 0.5 mm. Comparing the numbers withthe assumptions to obtain the graph in FIG. 8, the thickness of thehousing wall 20 appears to be smaller than the casing 50. Note that itis possible to achieve acceptable transmission loss by selecting anappropriate acoustic absorption layer 60.

As was indicated earlier, the material for the acoustic absorption layer60 may comprise foam, cork, sponge, rubber, or spray-on siliconecoating. According to an embodiment of the invention, the acousticabsorption layer 60 is a viscoelastic layer with possible voids, and ischaracterized by being light with slow sound speed. In other words, theacoustic absorption layer 60 has a acoustic impedance characteristicswhich are much smaller that that of the casing 50 and the housing wall20 or the cover member 40.

According to another embodiment of the invention, as shown in FIG. 10A,the MEMS microphone package 100 d has a substrate 10 on which a MEMSacoustic sensing element 3, an IC chip 4 and passive component 5 aremounted. An acoustic cavity 6 is formed by the substrate 10, housingwall 20 and a cover member 40. The attachment of the housing wall 20 andthe cover member 40 to the substrate 10 is realized by using glue 30which is applied between the substrate 10 and the housing wall 20, andbetween the housing the wall 20 and the cover member 40. The height ofthe housing wall 20 is large enough such that there is enough clearance11 between the top surface of MEMS sensing element 3 and the covermember 40. Soldering pads 2 are formed at the bottom of the substrate 10to allow the packaged MEMS microphone to be surface mountable onto a PCBmother board 70. The substrate 10 is made of FR-4 material to match thethermal property of a PCB mother board 70. An opening 1B is cut out fromboth the substrate 10 and a PCB mother board 70 to allow acousticsignals to pass therethrough to reach the surface of the MEMS sensingelement 3. In one embodiment, the opening 1B is formed in and extendedthrough the substrate 10. The opening 1B comprises an acoustic passageconnecting the acoustic cavity 6 to an ambient space. The location ofthe opening 1B is chosen such that it is away from the sensing element 3to protect dust from falling onto or moisture, such as from the mouth ofa human, to reach the surface of the sensing element 3. An acousticsealing layer 80 is coated around the outer edge of the opening 1B toseal the gap between the substrate 10 and a PCB mother board 70.According to another embodiment of the invention, the acoustic sealinglayer 80 is a metal solder bump, epoxy filler or rubber.

Referring to FIG. 10A further, a casing 50 surrounds and encloses themicrophone package. An acoustic absorption layer 60 is inserted betweenthe microphone housing wall 20 and/or top cover member 40 and the casing50. The casing 50 is not directly connecting to either the analog ordigital ground of the microphone package. It is instead electricallyconnecting to a common analog ground lead on a PCB mother board 70through soldering pads 52.

FIG. 10B is a cross section of another embodiment of the MEMS microphonepackage. In FIG. 10B, a MEMS microphone package 100 e includes a casing150 a with a conductive part disposed over a substrate 10 (also referredto as a MIC substrate), to enclose a cavity 11. The casing 150 a can bea unitary metal casing attached onto the substrate 10 by using aconductive glue 30. A MEMS acoustic sensing element 3, an IC chip 4, andat least one passive component 5 can be disposed inside the cavity 11.An opening 1B is formed in and extended through the substrate 10,wherein an acoustic opening formed in and extended through the PCBmother board 70 is aligned with the opening to allow acoustic signals topass therethrough. A first ground pad 130 (also referred to as an analogground pad) is disposed on a backside of the substrate 10 connecting tothe conductive part of the casing 150 a through a via hole 120 (e.g., athrough silicon via (TSV)) in the substrate 10. A second ground pad 140(also referred to as a digital ground pad) is disposed on the backsideof the substrate 10 connecting to the MEMS acoustic sensing element 3 orthe IC chip 4 through an interconnection 160 or a redistribution line(RDL) embedded in the substrate 10, wherein the first ground pad 130 andthe second ground pad 140 are isolated from each other. Since thedigital signal and environmental interference are respectively grounded,cross talk effect and environmental electromagnetic interference (EMI)noise can be eliminated. Therefore, a clean and clear acoustic signalcan be received by the MEMS microphone package 100 e.

In one embodiment of the invention, the substrate 10 is soldered onto aPCB mother board 70 (also referred to as a system PCB board), whereinthe first and second ground pads 130 and 140 are soldered to a commonground pad 170 on the PCB mother board 70. In another embodiment of theinvention, the substrate 10 is soldered onto a PCB mother board 70,wherein the first and second ground pads 130 and 140 are soldered torespective different ground pads on the PCB mother board. Other contactpads 135 on the backside of the substrate 10 can be soldered withcorresponding solder pads 175 on the PCB mother board 70.

FIG. 10C is a cross section of another embodiment of the MEMS microphonepackage. In FIG. 10C, a MEMS microphone package 100 f includes a casing150 b with a conductive part disposed over a substrate 10 (also referredto as a MIC substrate), to enclose a cavity 11. The casing 150 b can bea multilayered casing attached onto the substrate 10 by using aconductive glue 30. The multilayered casing 150 b can include a topcover part 155 and a housing wall part 153 surrounding and supportingthe top cover part. In another embodiment, the multilayered casing canincludes a conductive layer 154 sandwiched between two non-conductivelayers 152 and 156. Note that the multilayered casing may furtherinclude an acoustic absorption layer lining the multilayered casing. AMEMS acoustic sensing element 3, an IC chip 4, and at least one passivecomponent 5 can be disposed inside the cavity 11. An opening is formedin and extended through the substrate, wherein an acoustic openingformed in and extended through the PCB mother board is aligned with theopening to allow acoustic signals to pass therethrough. A first groundpad 130 is disposed on a backside of the substrate 10 connecting to theconductive part of the casing 150 b through a via hole 120 (e.g., athrough silicon via (TSV)) in the substrate 10. A second ground pad 140is disposed on the backside of the substrate 10 connecting to the MEMSacoustic sensing element 3 or the IC chip 4 through an interconnection160 or a redistribution line (RDL) embedded in the substrate 10, whereinthe first ground pad 130 and the second ground pad 140 are isolated fromeach other.

In one embodiment of the invention, the substrate 10 is soldered onto aPCB mother board 70, wherein the first and second ground pads 130 and140 are soldered to a common ground pad 170 on the PCB mother board 70.In another embodiment of the invention, the substrate 10 is solderedonto a PCB mother board 70, wherein the first and second ground pads 130and 140 are soldered to respective different ground pads on the PCBmother board. Other contact pads 135 on the backside of the substrate 10can be soldered with corresponding solder pads 175 on the PCB motherboard 70

According to further another embodiment of the invention, as illustratedin FIG. 11A, the MEMS microphone package 100 g has a substrate 10 onwhich a MEMS acoustic sensing element 3, an IC chip 4 and passivecomponent 5 are mounted. An acoustic cavity 6 is formed by the substrate10, housing wall 20 and a cover member 40. The attachment of the housingwall 20 and the cover member 40 to the substrate 10 is realized usingglue 30 which is applied between the substrate 10 and the housing wall20, and between the housing wall 20 and the cover member 40. The heightof the housing wall 20 is large enough such that there is enoughclearance 11 between the top surface of MEMS sensing element 3 and thecover member 40. Soldering pads 2 are formed at the bottom of thesubstrate 10 to allow the packaged MEMS microphone to be surfacemountable onto a PCB mother board 70. The substrate 10 is made of FR-4material to match the thermal property of a PCB mother board 70. Anopening 1B is cut out from both the substrate 10 and a PCB mother board70 to allow acoustic signals to pass therethrough to reach the surfaceof MEMS sensing element 3. The opening 1B is chosen to be disposed rightunder the MEMS sensing element 3. A screen 8 is provided between theMEMS sensing element 3 and the opening 1. The screen 8 is a perforatedplate having acoustic holes ranging from 10 micrometers to 50micrometers. According to another embodiment of the invention, thethickness of the screen 8 is from 10 micrometers to 100 micrometers.

According to further another embodiment of the invention, an acousticsealing layer 80 is coated around the outer edge of the opening 1 toseal the gap between the substrate 10 and a PCB mother board 70. Theacoustic sealing layer 80 is a metal solder bump, epoxy filler orrubber.

Referring to FIG. 11 further, a casing 50 surrounds and encloses themicrophone package. An acoustic absorption layer 60 is inserted betweenthe microphone housing wall 20 and/or top cover member 40 and the casing50. The casing 50 is not directly connecting to either the analog ordigital ground of the microphone package, it is instead electricallyconnecting to a common analog ground lead on a PCB mother board 70through the soldering pads 52.

Some embodiments of the micromachined MEMS microphone package areadvantageous in that acoustic leakage through side walls and the coverof the micromechined MEMS microphone package are effectively reduced. Byconnecting the conductive casing to the supporting PCB substrate, thebonding strength of the microphone package is strengthened. Also, theMEMS microphone package is not vulnerable to temperature fluctuationsduring the packaging and assembly process. Furthermore, due to theconductive casing that is electrically connecting to a common analogground lead of a supporting PCB mother board, electromagneticinterferences are shielded from the sensing element.

FIG. 11B is a cross section of another embodiment of the MEMS microphonepackage. In FIG. 11B, a MEMS microphone package 100 h includes a casing150 a with a conductive part disposed over a substrate 10 (also referredto as a MIC substrate), to enclose a cavity 11. The casing 150 a can bea unitary metal casing attached onto the substrate 10 by using aconductive glue 30. A MEMS acoustic sensing element 3, an IC chip 4, andat least one passive component 5 can be disposed inside the cavity 11.An opening 1B is formed in and extended through the substrate, whereinan acoustic opening formed in and extended through the PCB mother boardis aligned with the opening to allow acoustic signals to passtherethrough. The MEMS acoustic sensing element 3 can be disposed on oneend of the opening 1B. A perforated plate 8 is interposed between theone end of the opening 1B and the MEMS acoustic sensing element 3.Optionally, an acoustic sealer surrounds the opening and is interposedbetween the substrate and the PCB mother board. A first ground pad 130(also referred to as an analog ground pad) is disposed on a backside ofthe substrate 10 connecting to the conductive part of the casing 150 athrough a via hole 120 (e.g., a through silicon via (TSV)) in thesubstrate 10. A second ground pad 140 (also referred to as a digitalground pad) is disposed on the backside of the substrate 10 connectingto the MEMS acoustic sensing element 3 or the IC chip 4 through aninterconnection 160 or a redistribution line (RDL) embedded in thesubstrate 10, wherein the first ground pad 130 and the second ground pad140 are isolated from each other. Since the digital signal andenvironmental interference are respectively grounded, cross talk effectand environmental electromagnetic interference (EMI) noise can beeliminated. Therefore, a clean and clear acoustic signal can be receivedby the MEMS microphone package 100 h.

In one embodiment of the invention, the substrate 10 is soldered onto aPCB mother board 70 (also referred to as a system PCB board), whereinthe first and second ground pads 130 and 140 are soldered to a commonground pad 170 on the PCB mother board 70. In another embodiment of theinvention, the substrate 10 is soldered onto a PCB mother board 70,wherein the first and second ground pads 130 and 140 are soldered torespective different ground pads on the PCB mother board. Other contactpads 135 on the backside of the substrate 10 can be soldered withcorresponding solder pads 175 on the PCB mother board 70.

FIG. 11C is a cross section of another embodiment of the MEMS microphonepackage. In FIG. 11C, a MEMS microphone package 100 i includes a casing150 b with a conductive part disposed over a substrate 10 (also referredto as a MIC substrate), to enclose a cavity 11. The casing 150 b can bea multilayered casing attached onto the substrate 10 by using aconductive glue 30. The multilayered casing 150 b can include a topcover part 155 and a housing wall part 153 surrounding and supportingthe top cover part. In another embodiment, the multilayered casing canincludes a conductive layer 154 sandwiched between two non-conductivelayers 152 and 156. Note that the multilayered casing may furtherinclude an acoustic absorption layer lining the multilayered casing. AMEMS acoustic sensing element 3, an IC chip 4, and at least one passivecomponent 5 can be disposed inside the cavity 11. An opening 1B isformed in and extended through the substrate, wherein an acousticopening formed in and extended through the PCB mother board is alignedwith the opening to allow acoustic signals to pass therethrough. TheMEMS acoustic sensing element 3 can be disposed on one end of theopening 1B. A perforated plate 8 is interposed between the one end ofthe opening 1B and the MEMS acoustic sensing element 3. Optionally, anacoustic sealer surrounds the opening and is interposed between thesubstrate and the PCB mother board. A first ground pad 130 (alsoreferred to as an analog ground pad) is disposed on a backside of thesubstrate 10 connecting to the conductive part of the casing 150 bthrough a via hole 120 (e.g., a through silicon via (TSV)) in thesubstrate 10. A second ground pad 140 (also referred to as a digitalground pad) is disposed on the backside of the substrate 10 connectingto the MEMS acoustic sensing element 3 or the IC chip 4 through aninterconnection 160 or a redistribution line (RDL) embedded in thesubstrate 10, wherein the first ground pad 130 and the second ground pad140 are isolated from each other.

In one embodiment of the invention, the substrate 10 is soldered onto aPCB mother board 70, wherein the first and second ground pads 130 and140 are soldered to a common ground pad 170 on the PCB mother board 70.In another embodiment of the invention, the substrate 10 is solderedonto a PCB mother board 70, wherein the first and second ground pads 130and 140 are soldered to respective different ground pads on the PCBmother board. Other contact pads 135 on the backside of the substrate 10can be soldered with corresponding solder pads 175 on the PCB motherboard 70.

While the invention has been described by way of example and in terms ofthe embodiments, it is to be understood that the invention is notlimited to the disclosed embodiments. To the contrary, it is intended tocover various modifications and similar arrangements (as would beapparent to those skilled in the art). Therefore, the scope of theappended claims should be accorded the broadest interpretation so as toencompass all such modifications and similar arrangements.

1. A MEMS microphone package, comprising: a casing with a conductivepart disposed over a substrate, to enclose a cavity; a MEMS acousticsensing element and an IC chip disposed inside the cavity; an openingcomprising an acoustic passage connecting the cavity to an ambientspace; a first ground pad disposed on a backside of the substrateconnecting to the conductive part of the casing through a via hole ofthe substrate; and a second ground pad disposed on the backside of thesubstrate connecting to the MEMS acoustic sensing element or the IC chipthrough an interconnection of the substrate, wherein the first groundpad and the second ground pad are isolated from each other.
 2. The MEMSmicrophone package as claimed in claim 1, wherein the substrate issoldered onto a PCB mother board, wherein the first and second groundpads are soldered to a common ground pad on the PCB mother board.
 3. TheMEMS microphone package as claimed in claim 1, wherein the substrate issoldered onto a PCB mother board, wherein the first and second groundpads are soldered to respective different ground pads on the PCB motherboard.
 4. The MEMS microphone package as claimed in claim 1, wherein thecasing is a unitary metal casing.
 5. The MEMS microphone package asclaimed in claim 1, wherein the casing is a multilayered casingincluding a top cover part and a housing wall part surrounding andsupporting the top cover part.
 6. The MEMS microphone package as claimedin claim 5, wherein the multilayered casing comprises a conductive layersandwiched between two non-conductive layers.
 7. The MEMS microphonepackage as claimed in claim 5, further comprising an acoustic absorptionlayer lining the multilayered casing.
 8. The MEMS microphone package asclaimed in claim 1, wherein the opening is formed in and extendedthrough the casing to allow acoustic signals to pass therethrough. 9.The MEMS microphone package as claimed in claim 2, wherein the openingis formed in and extended through the substrate, wherein an acousticopening formed in and extended through the PCB mother board is alignedwith the opening to allow acoustic signals to pass therethrough.
 10. TheMEMS microphone package as claimed in claim 9, wherein the MEMS acousticsensing element is disposed on one end of the opening.
 11. The MEMSmicrophone package as claimed in claim 10, further comprising aperforated plate interposed between the one end of the opening and theMEMS acoustic sensing element.
 12. The MEMS microphone package asclaimed in claim 9, further comprising an acoustic sealer surrounds theopening and is interposed between the substrate and the PCB motherboard.
 13. The MEMS microphone package as claimed in claim 1, furthercomprising at least one passive element disposed inside the cavity. 14.A method for fabricating a MEMS microphone package, comprising:providing a substrate; forming a MEMS sensing element and an IC chip onthe substrate; disposing a casing with a conductive part on thesubstrate, to enclose a cavity to accommodate the MEMS sensing elementand the IC chip; forming an opening comprising an acoustic passageconnecting the cavity to an ambient space; connecting the conductivepart of the casing to a first ground pad on the backside of thesubstrate through a via hole; and connecting the MEMS acoustic sensingelement or the IC chip to a second ground pad on the backside of thesubstrate through an interconnection, wherein the first ground pad andthe second ground pad are isolated from each other.
 15. The method asclaimed in claim 14, wherein the substrate is soldered onto a PCB motherboard, and the first and second ground pads are soldered to a commonground pad on the PCB mother board.
 16. The method as claimed in claim14, wherein the substrate is soldered onto a PCB mother board, and thefirst and second ground pads are soldered to respective different groundpads on the PCB mother board.
 17. The method as claimed in claim 14,wherein the casing is a unitary metal casing.
 18. The method as claimedin claim 14, wherein the casing is a multilayered casing including a topcover part and a housing wall part surrounding and supporting the topcover part.
 19. The method as claimed in claim 18, wherein themultilayered casing comprises a conductive layer sandwiched between twonon-conductive layers.
 20. The method as claimed in claim 18, furthercomprising an acoustic absorption layer lining the multilayered casing.21. The method as claimed in claim 14, wherein the opening is formed inand extended through the casing to allow acoustic signals to passtherethrough.
 22. The method as claimed in claim 15, wherein the openingis formed in and extended through the substrate, and an acoustic openingformed in and extended through the PCB mother board is aligned with theopening to allow acoustic signals to pass therethrough.
 23. The methodas claimed in claim 22, wherein the MEMS acoustic sensing element isdisposed on one end of the opening.
 24. The method as claimed in claim23, further comprising a perforated plate interposed between the one endof the opening and the MEMS acoustic sensing element.
 25. The method asclaimed in claim 22, further comprising an acoustic sealer surrounds theopening and is interposed between the substrate and the PCB motherboard.
 26. The method as claimed in claim 14, further comprising atleast one passive element disposed inside the cavity.